Self-modulating air moving device



April 23, 1963 F. M. DONNELLY SELF-MODULATING AIR MOVING DEVICE 3 Sheets-Sheet 1 Filed Feb. 5, 1962 ATTORN EYS- April 1963 F. M. DONNELLY 3,086,699

SELF-MODULATING AIR MOVING DEVICE 3 Sheets-Sheet 2 Filed Feb. 5, 1962 4 L I INVENTOR.

' F2 KMDo ELL, Fig-6 W W ATTORNEYS April 23, 1963 F. M. DONNELLY 3,085,699

SELF-MODULATING AIR MOVING DEVICE Filed Feb. 5, 1962 a Sheets-Sheet 3 INVENTOR. F m M. NNE LY, 132W W 'v ATTORNEYS- United rates Fatent 3,0865% SELF-MGDULATING AIR MGVING DEVEQE Frank M. Donneiiy, incinnati, Ghio, assignor to Belmont Blower Corporation, Cincinnati, Ohio, a corporation of (Bhio Filed Feb. 5, 1962, Ser. No. 170,833 17 (Iiaims. (Ql. 230-117) This invention relates to an air moving device for exhausting air from an enclosed space and discharging it to atmosphere. More particularly, the invention relates to an air moving device of high efficiency which can maintain a relatively constant suction on the exhaust hood of a kitchen range or the like at elevated temperatures.

Although conventional centrifugal type blowers are capable of exhausting air from a room or enclosure with good suction at ordinary room temperatures, at elevated temperatures (on the order of 2S045 F. or higher), such as are encountered in exhausting combustion gases, fumes, vaporized grease, etc. from a kitchen range hood, this suction drops very markedly due to the decrease in density in the air or other gases being exhausted. A centrifugal blower could be designed to produce the desired suction at elevated temperatures, but it would be inetficient at ordinary room temperatures.

Attempts to design an air moving device utilizing Bernoullis principle (also referred to as the Jet Pump principle), wherein a constant externally introduced air stream of high velocity at the throat of an expanding section of duct tends to induce a suction on the intake side so as to draw out a volume of air inversely proportional to the density of air within the duct, have been unsuccessful due to the necessarily low mechanical etficiency of such an arrangement. The eficiency of such a device is low regardless of whether it is exhausting air at ordinary room temperatures or at elevated temperatures.

There has therefore been a long standing need for an air moving device which can operate at a relatively constant high efiiciency throughout the temperature ranges encountered in kitchen range hoods and like structures, particularly the larger types of ranges and ovens used in institutions, restaurants, bakeries and the like. It will of course be understood that a drop in the efiiciency of an air moving device at elevated temperatures greatly increases the hazard of fires resulting from heated vaporized grease.

Accordingly, it is a principal object of the present invention to provide a self-modulating air moving device which can operate at relatively constant high efliciency over a wide temperature range.

It is a further object of the invention to provide a selfmodulating air moving device which can readily be dis assembled without special tools for cleaning of the ducts and the blower wheel.

It is another object of the invention to provide an air moving device which prevents precipitation from entering the vent of a range hood without the necessity for providing closable louvers or shutters on the outside surface thereof.

Briefiy stated, the present invention comprises a combination of an air stream of high velocity at the throat of an expanding section of duct with a centrifugal blower wheel open on both sides for passage of air therethrough in either direction. At ordinary room temperatures the centrifugal blower wheel operates to exhaust air through the throat and expanding duct section at high etficiency as a result of the novel concept of utilizing a part of the air being exhausted to create the let Pump effect at the throat. At higher temperatures cooler outside air is supplied to the wheel, drawn into the wheel and passed centn'fugally outwardly so as to maintain the velocity of the air passing through the throat at a substantially constant value. It has been found that the wheel automatically modulates a balance between the relative amounts of heated exhaust air and cooler outside air drawn through the wheel as the temperature of the air or gases being exhausted varies. Thus a surprisingly high efficiency is obtained when air of ordinary room temperature is being exhausted, and this efliciency is maintained at a satisfactory level as the temperature of the air being exhausted increases by reason of the gradual self-modulated increase in the amount of cool outside air drawn into the Wheel and forced outwardly through the throat and expanding duct section, thereby maintaining the equivalent of an area of low pressure below and adjacent the inlet for the exhaust gases. At the same time certain critical design features must be observed in order to obtain optimum efiiciency, as will be hereinafter explained.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as forming the present invention, it is believed that the invention will be better understood from the following description taken in connection with the accompanying drawings in which:

FIGURE 1 is a cross sectional view, partly diagrammatic, of a preferred embodiment of the invention;

FIGURE 1a is an enlarged fragmentary view of a portion of FIGURE 1, showing the mounting of the electric motor;

FIGURE 2 is a cross sectional view taken line 22 of FIGURE 1;

FIGURE 3 is a fragmentary perspective view of the embodiment of FIGURE 1 showing the parts in exploded relation;

FIGURE 4 is a perspective view of one type of centrifugal blower wheel suitable for use in the present invention;

FIGURE 5 is a perspective view of another type of centrifugal blower wheel suitable for use in the present invention;

FIGURE 6 is a perspective view of another type of centrifugal blower wheel suitable for use in the present invention;

FIGURE 7 is a cross sectional view, partly diagrammatic, of another embodiment of the invention; and

FIGURE 8 is a perspective view of a preferred type of centrifugal blower wheel suitable for use in the present invention.

Referring to FIGURE 1, there is shown a horizontally disposed curb base 1 which is secured in place in a conventional manner on a roof above the vent of a kitchen range hood or like structure from which heated air, combustion gases, fumes, vaporized grease, etc., are to be exhausted. It will of course be understood that the utility of the invention is not so limited but that the device is efieotive in any application Where it is desired to exhaust air or gases from an enclosed space. In the base 1 is formed a circular inlet opening 2 for air which is to be exhausted communicating directly with the vent of a range hood (not shown). Preferably the edge of the inlet opening is flared upwardly, as shown at 3, for a purpose hereinafter described. Mounted on the base It, and secured thereto by welding or other conventional means, is a windband or drum 4 of circular cross section. The Windband is concentric with the inlet opening 2, and in the preferred embodiment of FIGURE 1, is of cylindrical shape. In the upper edge of the windband three slots 5, 6 and 7 (as best seen in FIGURE 3) are provided. Two of the slots 5 and 7 are disposed opposite each other l apart While the slot 6 is intermediate therebetween. Slots 5 and 7 are adapted to receive bypass or outside air conduits 8 and 9, which extend bealong the yond the edge of the windband. The conduits may be circular, square or rectangular in cross section, and it will be understood that the slots and 7 will have correspondingly matching configurations. Each conduit terminates in a downwardly facing outside air inlet covered by a screen (not shown).

The by-pass air conduits 8 and 9 which range from 3 to 12 square inches in'cross sectional area conduct outside air to the interior of the motor housing (indicated generally at '11) to which they are secured near the top thereof. This housing consists of a flat top portion 12, a sidewall .13 of frusto-conical configuration in the embodiment of FIGURE 1 and a generally bowl-shaped base portion 1 4. The housing is concentric with the inlet opening andv windband, and in assembled relation the top of the housing is just below the top edge of the windband.

Slot 6 is adapted to receive an electrical connection conduit 15 which has the same diameter as the by-pass air conduits. The conduit 15 also extends beyond the edge of the windband but terminates in a closed cap having a right angle electrical junction 16 to which a flexible electric cable 17 is connected. This cable is of the type sold under the registered trademark Sealtite. The cable hangs downwardly in a slack loop from the junction 16 and runs 90 around the base of the windband whereit is connected to a junction box 18 positioned several inches above the bottom of the windband beneath slot 5. From the junction 16 insulated electrical leads pass through the conduit 15 and down into the interior of the housing to the electric motor, indicated diagrammatically at 19.

The motor may be of any conventional type adapted to rotate at 850, L150, 1750 or 3500 rpm. In most installations a speed of 3500 r.p.m. is preferred. The motor is mounted by bolts on a motor mounting plate 20. The mounting plate 20 has a configuration generally similar to that of the motor housing base portion 14. As shown in FIGURES 1 and 1a the mounting plate is secured to the housing base portion by rubber vibration pads 21 through each of which pass a bolt 22 fastened by a nut 23. Several rubber vibration pads are provided, and these serve to isolate the rotating parts from the stationary parts;

The mounting plate 20 is mounted in such a way as to leave a clearance of from inch to 1 inch between it and the base portion of the housing and is so constructed that it will permit bypass air drawn through conduits 8 and 9 to flow around the motor and through a circular orifice 24- formed in the center of the base portion of the housing.

The orifice 24, through which the motor shaft 25 also extends, is of smaller diameter than the exhaust air inlet 2.

A centrifugal blower wheel, indicated generally at 26, is mounted on the shaft 25 directly beneath the orifice 24 and is of greater diameter than orifice 24. Details of the blower wheel will be described hereinafter.

The periphery of the base portion 14 of the motor housing is upturned at an angle of from 15 to 40 from the horizontal as shown at 27. The preferred angle is about and it has been found that this upturned periphery is essential in order to permit the wheel to impart an upward vector of kinetic energy to the air forced centrifugally outwardly by its blades. Preferably the that central section of the base portion of the housing is of approximately the same diameter as the blower wheel.

The upturned periphery 27 is provided with a plurality of screw holes around its edge through which sheet metal screws 28 may be threaded. The extreme outer edge of the periphery is turned downwardly as shown at 27a so as to fit inside the lowermost edge of the sidewall 13. The sidewall 13 is provided with a plurality of brackets 29 secured about A inch from its lower edge,

each of which has a screw hole mating with one in the periphery 27. The base portion may thus be secured to the sidewall by the sheet metal screws 28. It will be noted that the lowermost edge 30 of the sidewall 13 extends a short distance below the heads of the screws, thereby providing a lip, the function of which will be described hereinafter.

A screen 31 made of hardware cloth or expanded metal is provided for covering the top of the windband. A downwardly dependingannular flange 32 is secured near the outer edge of the screen, of a diameter permitting it to fit snugly either inside or outside the edge of the windband. Four threaded holes 33, each apart radially, are provided in the flange and four mating holes 34 are formed near the top edge of the windband, two of which are between the slots 5, 6 and 7. Four thumb screws 35 are provided to secure the screen to the windband by threading them through the mating holes 33 and 34. The flange 32 has a width such that it will contact the top surfaces of the conduits 8, 9 and 15 and restrain them from moving either upwardly or laterally in the slots. Since there are three conduits of circular cross section engaged in U-shaped slots in the embodiment of FIGURES 1-3, this provides a positive means for preventing rocking or movement of the motor housing relative to the windband.

About 4 inch above the curb base 1 one or more drain holes 36 are provided for removal of precipitation which enters through the screen when the air moving device is not in operation. These drain holes are located in an area of pressure differential between the inside and outside of the windband, which ensures purging of the holes. The upwardly flared edge 3 of the exhaust air inlet 2 prevents precipitation from running down into the vent from the range hood. By positioning the drain hole or holes 36 slightly above the horizontal curb base 1 a shallow pool of water may be maintained inside the windband, as shown at 37, which will tend to cool sudden short surges of heated gases which may pass through the inlet 2. Tubes or other conventional means (not shown) may be provided to conduct water from the holes 36 to .a convenient discharge point.

The lowermost edge 30 of the housing sidewall 13 forms a lip which has two functions. First, it provides a rim from which precipitation will drip into the pool 37, when the device is not operating, thereby preventing moisture from getting up into the base portion 14 of the housing. The downturned edge 27a of the base portion is so constructed as to mate with the edge 30, thereby placing any opening therebetween in an area of high velocity which will create a negative pressure at that point to prevent fumes and vaporized grease from entering the motor housing Second, the lip produces an improvement in the induced air flow from the blower wheel. It is believed that this effect is obtained by the creation of a layer of static air held by the lip 30 upon the surface of the upturned periphery 27 of the base portion of the housing, thereby creating a cushion over which the induced air flow passes smoothly.

The various types of centrifugal blower Wheels which are suitable for use in the present invention are illustrated in FIGURES 4-6 and 8. In FIGURE 4, a backward-curve wheel 26a is shown, having blades 38 which are inclined away from the direction of rotation of the wheel. Spokes 39 are provided on each side of the hub 40 to support the inclined rim 41 on each side of the blades. The central portion of the wheel is thus open on both sides so as to permit passage of air therethrough in either direction. FIGURE 5 illustrates a forwardcurve wheel 26]; having blades 42 which are inclined at an angle toward the direction of rotation of the wheel. Here again, spokes 43' are provided on each side of the hub 44 to support the rim 45 on each side of the blades. Thus the central portion of the wheel is open so as to permit passage of air therethrough in either direction. FIGURE 6 discloses a radial wheel 260 having blades .6 extending radially outwardly from the hub 47 and secured thereto. A rim 48 is provided on one side of the blade in order to rigidify the structure. Here again, the central portion of the Wheel is open so as to permit passage of air therethrough in either direction. FI URE 8 discloses a preferred type of radial wheel 26:! having a central web 49, from the outer portion of which depend a plurality of radial angularly inclined blades 5!). The outer edges of the blades form an angle of approximately 30 with the vertical, so that the edges of the blades are approximately at right angles to the upturned periphery 27 of the base portion of the housing. The central Web has a plurality of V-shaped openings 51 through which m'r may pass in either direction. This wheel may be made inexpensively from 12 gauge sheet metal, and if desired the central web may have Welded thereto a similarly shaped reinforcing member of the same gauge sheet metal having V-shaped openings which mate with those of the central web. The performance characteristics of the radial centrifugal blower wheel of FIGURE 8 have been found to be superior. The maximum diameter of the Wheel of FIGURE 8 will be about the same as the diameter of the wheels illustrated in FIG- URES 4-6, and hence the maximum diameter of the wheel 26d will be greater than the diameter of the orifice 24 in the base portion 14 of the housing but will be smaller than the diameter of the exhaust air inlet 2.

Regardless of the type of wheel used, the maximum diameter should in all instances be greater than the diameter of the orifice 24 in the base portion of the motor housing 14 and smaller than the exhaust air inlet 2, and it is essential that the wheel be open to passage of air completely through the wheel from one side to the other in either direction. Preferably the hub of the wheel will be designed in such a manner that it cannot be installed on the shaft 25 in an improper manner. This can be accomplished by controlling the location and/or length of the shaft relative to the hub of the wheel.

As indicated previously, in the preferred embodiment of FIGURE 1, the sidewall 13 is of frusto-conical shape, and the ratio of the diameter of the sidewall at its lower edge, where it is secured to the base portion 14, to the diameter of the windband or drum is a critical feature of the instant invention, as is the angle of divergence between the sidewall and the cylindrical windband. The exponential ratio of the diameter of the sidewall at its lower edge to the diameter of the windband should be between a power of 0.85 and 0.992, the preferred range being between a power of 0.85 and 0.97. The diverging sidewall and windband form an expanding discharge section 52 above the relatively restricted throat 53. The included angle of divergence between the sidewall and the windband should be between 3 /2 and 22 /2, the preferred range being between 7 /2 and In the embodiment of FTGURE 7, it will be observed that the essential structural features set forth above are also incorporated. in this embodiment, however, the circular windband or drum 4a is of inverted frusto-conical shape, while the sidewall 13a of the motor housing is of cylindrical shape. Like parts are indicated by similar characters of reference in the two embodiments. The exponential ratio of the diameter of the sidewall to the diameter of the windband in the horizontal plane passing through the lower edge of the sidewall is within a power of from 0.85 to 0.992 in the embodiment of FIG- URE 7. The proportionate size of the relatively restricted throat 53 is thus the same as the size of the throat 53 in the embodiment of FIGURES 1-3, while the angle of divergence of the sidewall from the windband, thereby forming the expanded discharge section 52, falls between 3 /2 and 22 /2". In all other respects, the embodiment of FIGURE 7 is identical to that of FIGURES 1-3, and hence need not be described in further detail.

It has been found that the following combination of structural features is essential to obtain the unique performance characteristics of the present device:

-(1) The diameter of the centrifugal blower wheel must be less than the diameter of the exhaust air inlet.

(2) The exponential ratio of the diameter of the sidewall of the motor housing at its lower edge to the diameter of the windband directly opposite this point (i.e. in a horizontal plane through the lower edge of the sidewall) must lie within a power of from 0.85 to 0.992.

3) The included angle of divergence between the sidewall of the motor housing and the windband, i.e. the expanding duct section above the throat, must be between 3 /2 and 22 /2 (4) The periphery of the base portion of the motor housing must be upturned at an angle of from 15 to 40 with the horizontal.

(5) The wheel must be open on both sides so that air can pass therethrough from one side to the other in both directions.

The omission of any one of the above structural features, or the modification thereof outside the ranges set forth above, have been found to impair the efiiciency of the air moving device to a serious degree.

In actual operation, rotation of the centrifugal blower wheel 26 draws a portion of the gases (indicated as A) to be exhausted through the central section of the inlet opening 2 and whirls it centrifugally outwardly and upwardly past the restricted throat 53 and expanding discharge duct 52, from which it is discharged to atmosphere through the screen 31. Since the diameter of the wheel is less than that of the inlet 2, the wheel tends to draw exhaust gases from the central portion of the inlet opening 2 directly beneath it and has less direct effect upon the exhaust gases at the peripheral section of the inlet opening 2. This portion A of the exhaust gases is given a high kinetic energy by the centrifugal blower wheel and hence moves at high velocity past the upwardly sloping periphery 27 of the housing base 14. As it passes the lip 30 and moves rapidly upwardly past the throat 53 and through the expanding duct 52, a Jet Pump eifect is produced, creating a suction in the area below and adjacent inlet opening 2. This area of subatmospheric pressure tends to draw additional gases to be exhausted (indicated as C) through the peripheral section of the exhaust gas inlet 2. The overall effect of these additional gases which are drawn upwardly around the outside of the wheel is to create a counterflow which opposes the wheels tendency to recirculate at its tip, which would, if permitted to occur greatly reduce operating efiiciency. The concept of using a portion of the gases to be exhausted to produce the Jet Pump effect with a considerable improvement in operating efiiciency is believed to be broadly new. If the air moving device is to be used solely for exhausting gases at ordinary room temperatures, it operates as a highly efiicient exhausting device.

So long as the temperature of the gases being exhausted does not increase appreciably above room temperature, very little, if any, outside air will be drawn in by the wheel 26 via conduits 8 and 9 through the interior of housing 11. However, if the temperature of the exhaust gases rises to any marked extent, the density of the exhaust gases decreases proportionately. This results in a decrease in the velocity and mass of the gases A being used to produce the Jet Pump effect. When this happens, the constant suction of the Wheel 26 draws a larger percentage of cooler and heavier outside air (indicated as B) through intakes 19, conduits 8 and 9, housing 11 and orifice 24 in the base portion 14 of the housing. This cooler air B is drawn through the rotating blower wheel and whirled centrifugally outwardly and upwardly, thereby supplementing the flow of high velocity exhaust gases. This therefore tends to maintain a relatively constant area of suction by means of the Jet Pump principle. The proportion of cooler outside air so drawn in by the wheel has been found to be automatically governed by any change in temperature of the exhaust gases. The present invention thus provides a self-modulating air moving device which balances the desired relative proportions of cooler outside air and heated exhaust gases within the wheel itself.

As will be apparent from FIGURE 3, the present device can readily be disassembled from the top thereof for cleaning or repair without tools of any kind. The four thumb screws 35 which secure the screen 31 and its annular flange 32 in place on top of the windband 4 can be unthreaded by hand. Thereafter the screen 31 is lifted upwardly and laid on the roof by the workman. The conduits 8, 9 and 15, the motor housing 11, motor 19 and centrifugal blower wheel 26 can then be lifted upwardly as an integral unit out of the slots 5, 6 and 7 of the windband 4 in which the conduits are received. The flexible electric cable 17 has sufiicient slack to permit the integral unit to be lifted high enough so that the wheel 26 will clear the top edge of the windband 4, and the assembly may then be laid on its side on the roof for cleaning or repair. It is not necessary to disconnect any of the electrical connections for this purpose.

It will of course be understood that deposits of grease and soot collect on the fans of the blower wheel, the sides of the motor housing and the interior of the windband 4. However, the design of the present device and the ready disassembly thereof make all the parts which require frequent cleaning readily accessible from the roof on which the device is mounted. Accessibility from the outside of the device is preferable to access from the range hood inside a kitchen.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable but which obviously is susceptible of modification in its form, proportions, detailed construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages. For example, while the conduits 8' and 9 have been shown in the drawings to be circular in cross section, conduits of square or rectangular cross section could be used, with slots and '7 in windband 4 having a matching shape. Conduit 8 could be used as the bypass air conduit by providing an air inlet of suitable area, and conduit 9 (180 apart radially) could be used as an electrical connection conduit, thereby eliminating the third conduit and slot. Since the square or rectangular conduits would be engaged firmly against turning by the slots of corresponding shape, the motor housing would not be able to move relative to the windband.

The invention having been described in exemplary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. An air moving device for exhausting air of varying density from an enclosure, comprising an electric motor, a centrifugal blower wheel mounted on the shaft of said motor for rotation in a horizontal plane, an inlet for exhaust air disposed beneath said wheel and of greater diameter than said wheel, a housing of circular cross-section surrounding the top, sides and bottom of said motor with clearance thereabout, at least one bypass air conduit communicating with the interior of said motor housing adjacent the top thereof, a windband of circular cross-section surrounding said housing and coaxial therewith, and a screen covering the outlet of said windband, said wheel being open on both sides whereby to permit air to pass therethrough from one side to the other in either direction, the wall of said motor housing surrounding the sides of the motor and said windband diverging with respect to one another, the included angle of divergence being between 3 /2 and 22 /2, the ratio of the diameter of said motor housing to the diameter of said windband in the plane of the nearest approach therebetween varying exponentially between a power of-0.85 and 0.992, the portion of said motor housing at the bottom of said 'motor having a circular opening through which said shaft extends of a diameter smaller than that of said Wheel, the periphery of said bottom portion of said housing being upturned at an angle of from 15 to 40 with the horizontal.

2. An air moving device as claimed in claim 1, in which said side wall of said motor housing is of frustoconical shape and in which the windband is cylindrical, the ratio of the maximum diameter of said side wall of said motor housing to the diameter of said windband varying exponentially between a power of 0.85 and 0.97, the included angle of divergence between said side wall of said motor housing and said windband being between 7.5 and 10.

3. In an air moving device for exhausting heated air from a kitchen range hood or the like, the combination of an electric motor, a centrifugal blower wheel mounted for rotation in a horizontal plane beneath said motor on the shaft thereof, said wheel permitting air to pass therethrough from one side to the other, an inlet for heated air beneath said wheel, said inlet having a greater diameter than said wheel, a housing of circular cross-section surrounding the top, sides and bottom of said motor with clearance thereabout, a source for introducing bypass air into said housing, and a windband of circular cross-section surrounding said housing and coaxial therewith, the wall of said housing surrounding the sides of said motor being of frusto-conical shape, the windband being of cylindrical shape, the exponential ratio of the maximum diameter of the side wall of said housing to the diameter of said windband varying between a power of 0.85 and 0.992 and the included angle of divergence between said side wall and said windband being from 3 /2 to 22 /z, said motor housing also having a bottom portion with an opening through which said shaft passes, the peripheral edge of said bottom portion being upturned to attach to said side wall at an angle of from 15 to 40 with the horizontal, and a flange around the lower portion of said side Wall extending below the point at which said bottom portion is attached to said side wall.

4. An air moving device for exhausting air of varying density from an enclosure, comprising a centrifugal blower wheel mounted on the shaft of an electric motor for rotation in a horizontal plane, said wheel being open on both sides to permit air to pass therethrough fiom one side to the other in either direction, a circular inlet for exhaust air of greater diameter than said wheel and disposed beneath said wheel, a housing of circular cross-section having a top, side wall and bottom portion surrounding the motor with clearance thereabout, the bottom portion of said housing having an opening therein for passage of the motor shaft therethrough and for passage of air within the housing to said wheel, the periphery of said bottom portion of said housing, at a point beyond the outer edge of said wheel, being upturned at an angle of from 15 to 40 with the horizontal, a pair of conduits secured to the upper portion of the sidewall of said housing on opposite sides thereof for admitting by-passing .air into said housing, a windband of circular cross-section surrounding said housing and coaxial therewith, said conduits extending through correspondingly shaped slots in the upper edge of said windband, the sidewall of said motor housing and said windband diverging from one another with an included angle of divergence of from 3 /2" to 22 /2, the ratio of the diameter of said housing to the diameter of said windband in the horizontal plane of the nearest approach between said housing and said windband varying exponentially between a power of 0.85 and 0.992, whereby to form a relatively constricted throat therebetween at said upturned periphery of said bottom portion of the housing and an expanding discharge passage thereabove,

a screen covering the top of said windband, and means for releasably securing said screen to said windband.

5. A device as claimed in claim 4, including an electrical connection conduit secured to the upper portion of the sidewall of said housing in the same plane as said bypass air conduits and extending outwardly at 90 thereto through an additional correspondingly shaped slot in the upper edge of said windband, all said conduits being circular in cross-section and said slots being U-shaped, and wherein said screen has a downwardly depending peripheral flange which contacts the top surfaces of said bypass air conduits and said electrical connection conduit, thereby placing said conduits and said housing under restraint against movement relative to said windband.

6. A device as claimed in claim 4, including means for securing the lower edge of said sidewall of the housing to the upturned periphery of said bottom portion of the housing, said sidewall projecting a short distance below said periphery so as to form a lip from which precipitation entering said windband through said screen will drop.

7. A device as claimed in claim 6, wherein said exhaust air inlet has an upwardly turned edge which acts to collect precipitation between said edge and the surrounding windband, and including at least one drain hole communicating with the interior of said windband for conducting said precipitation outside thereof for discharge at a convenient point.

8. A device as claimed in claim 6, including a horizontally disposed curb base of sheet metal on which said windband is mounted, said exhaust air inlet being formed in said curb base, the sheet metal around said inlet opening being upturned to form a reservoir between said opening and the surrounding windband for collection of precipitation entering the interior of the windband through said screen, and at least one drain hole mounted above said curb base and communicating with said reservoir for conducting collected precipitation to discharge outside said windband.

9. A device as claimed in claim 8, wherein said drain hole is located in an area of pressure differential between the inside and outside of said windband, whereby to ensure purging thereof.

10. A device as claimed in claim 5, wherein said means for releasably securing said screen to said windband comprise a plurality of thumb screws engageable in threaded mating holes in said windband and said peripheral flange, the arrangement being such that upon removal of said thumb screws said screen can be lifted upwardly away from said windband, and thereafter said motor housing, motor, blower wheel, by-pass air conduits and electrical connection conduit can be lifted as a unit upwardly from said windband.

11. A device as claimed in claim 10, including a flexible electrical cable extending from the end of said electrical connection conduit to an electrical junction box positioned near the base of said windband beneath one of said bypass air conduits, said cable having sufiicient slack to permit said conduits, motor housing, motor and blower wheel to be lifted upwardly from said windband.

12. A device as claimed in claim 4, in which said centrifugal blower wheel has radial blades.

13. A device as claimed in claim 12, in which the edges of said radial blades are inclined at an angle of about 30 to the vertical.

14. A device as claimed in claim 4, in which said centrifugal blower wheel has forwardly-curved blades.

15. A device as claimed in claim 4, in which said centrifugal blower wheel has backwardly-curved blades.

16. An air moving device for exhausting air of varying density from an enclosure, comprising a centrifugal blower wheel mounted on the shaft of an electric motor for rotation in a horizontal plane, said wheel being open on both sides to permit air to pass therethrough from one side to the other in either direction, a circular inlet for exhaust air of greater diameter than said Wheel and disposed beneath said wheel, a housing of circular cross-section having a top, sidewall and bottom portion surrounding the motor with clearance thereabout, the bottom portion of said housing having an opening therein for passage or" the motor shaft therethrough and for passage of air within the housing to said wheel, the periphery of said bottom portion of said housing, at a point beyond the outer edge of said wheel, being upturned at an angle of from 15 to 40 with the horizontal, a pair of conduits of quadrilateral cross-section secured to the upper portion of the sidewall of said housing on opposite sides thereof apart radially, said conduits communicating with the interior of said housing, one of said conduits terminating in a downwardly facing opening having a screen therein through which outside air may be drawn into the housing and the other conduit being an electrical connection conduit through which leads run to said electric motor, a windband of circular cross-section surrounding said housing and coaxial therewith, said conduits extending through slots in the upper edge of said windband, said slots having a configuration and dimension which will permit said conduits to be received snugly therein, the sidewall of said motor housing and said windband diverging from one another with an included angle of divergence of from 3 /2 to 22 /2 the ratio of the diameter of said housing to the diameter of said windband in the horizontal plane extending through the lowermost edge of the sidewall of said housing and said windband varying exponentially between a power of 0.85 and 0.992, whereby to form a relatively constricted throat therebetween at said upturned periphery of said bottom portion of the housing and an expanding discharge passage thereabove, a screen covering the top of said windband, and means for releasably securing said screen to said windband.

17. A device as claimed in claim 16, wherein said screen has a downwardly depending peripheral flange which contacts the top edges of said conduits, thereby placing said conduits and said housing under restraint against movement relative to said windband.

References Cited in the file of this patent UNITED STATES PATENTS 2,931,560 Court Apr. 5, 1960 

1. AN AIR MOVING DEVICE FOR EXHAUSTING AIR OF VARYING DENSITY FROM AN ENCLOSURE, COMPRISING AN ELECTRIC MOTOR, A CENTRIFUGAL BLOWER WHEEL MOUNTED ON THE SHAFT OF SAID MOTOR FOR ROTATION IN A HORIZONTAL PLANE, AN INLET FOR EXHAUST AIR DISPOSED BENEATH SAID WHEEL AND OF GREATER DIAMETER THAN SAID WHEEL, A HOUSING OF CIRCULAR CROSS-SECTION SURROUNDING THE TOP, SIDES AND BOTTOM OF SAID MOTOR WITH CLEARANCE THEREABOUT, AT LEAST ONE BYPASS AIR CONDUIT COMMUNICATING WITH THE INTERIOR OF SAID MOTOR HOUSING ADJACENT THE TOP THEREOF, A WINDBAND OF CIRCULAR CROSS-SECTION SURROUNDING SAID HOUSING AND COAXIAL THEREWITH, AND A SCREEN COVERING THE OUTLET OF SAID WINDBAND, SAID WHEEL BEING OPEN ON BOTH SIDES WHEREBY TO PERMIT AIR TO PASS THERETHROUGH FROM ONE SIDE TO THE OTHER IN EITHER DIRECTION, THE WALL OF SAID MOTOR HOUSING SURROUNDING THE SIDES OF THE MOTOR AND SAID WINDBAND DIVERGING WITH RESPECT TO ONE ANOTHER, THE INCLUDED ANGLE OF DIVERGENCE BEING BETWEEN 3 1/2* AND 22 1/2*, THE RATIO OF THE DIAMETER OF SAID MOTOR HOUSING TO THE DIAMETER OF SAID WINDBAND IN THE PLANE OF THE NEAREST APPROACH THEREBETWEEN VARYING EXPONENTIALLY BETWEEN A POWER OF 0.85 AND 0.992, THE PORTION OF SAID MOTOR HOUSING AT THE BOTTOM OF SAID MOTOR HAVING A CIRCULAR OPENING THROUGH WHICH SAID SHAFT EXTENDS OF A DIAMETER SMALLER THAN THAT OF SAID WHEEL, THE PERIPHERY OF SAID BOTTOM PORTION OF SAID HOUSING BEING UPTURNED AT AN ANGLE OF FROM 15* TO 40* WITH THE HORIZONTAL. 